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Operational Modal Analysis of A Bridge

The operational modal analysis of a sea-crossing bridge presented here is performed for structural health monitoring (SHM) using ModalVIEW software as the modal analysis tool. The analysis result provides quantitative data of the bridge for accessing extent of damages/deterioration, evaluating the structural performance .

Measured Data

The following figure shows the measured time records with 50Hz sampling rate from 14 measured points:

To identify modes of this bridge structure from its operating data, operational modal analysis method of stochastic subspace identification (SSI) is used. ModalVIEW modal analysis software provides advanced SSI method based on mode stabilization diagram to extract modes from time records.  

Analysis results

Modal analysis for the structure is finished with ModalVIEW’s advanced SSI mode estimation method based on mode stabilization diagram.The following figure shows the clear mode stabilization diagram from 14 measured time records.

The modes are selected from stabilization diagram. The real modes are kept with mathematical or faked modes being discarded. Part of the picked meaningful modes are listed in following table :

Index Frequency (Hz) Damping (%)
1 0.367411 0.776547
2 0.503365 0.746528
3 0.634541 0.22159
4 0.780597 0.416912
5 0.997976 0.820229
6 1.03676 0.337842
7 1.26534 0.583239
8 1.38638 0.723831

One of the mode shapes is displayed as following :

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Last updated Jan 1st, 2017